linux-kernel - Re: [PATCH v2 1/1] s390/spinlock: Provide vcpu_is

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Message-Id: <20161019074448.GC4077@osiris>
Date:   Wed, 19 Oct 2016 09:44:48 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        xen-devel-request@...ts.xenproject.org, benh@...nel.crashing.org,
        paulus@...ba.org, mpe@...erman.id.au, mingo@...hat.com,
        paulmck@...ux.vnet.ibm.com, will.deacon@....com,
        kernellwp@...il.com, jgross@...e.com, pbonzini@...hat.com,
        bsingharora@...il.com
Subject: Re: [PATCH v2 1/1] s390/spinlock: Provide vcpu_is_preempted

On Wed, Oct 19, 2016 at 08:56:36AM +0200, Christian Borntraeger wrote:
> On 09/29/2016 05:51 PM, Christian Borntraeger wrote:
> > this implements the s390 backend for commit
> > "kernel/sched: introduce vcpu preempted check interface"
> > by reworking the existing smp_vcpu_scheduled into
> > arch_vcpu_is_preempted. We can then also get rid of the
> > local cpu_is_preempted function by moving the
> > CIF_ENABLED_WAIT test into arch_vcpu_is_preempted.
> > 
> > Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
> 
> 
> Martin, Peter,
> 
> I think we could go with the patch as is. In other words not providing
> arch_vcpu_is_preempted for !CONFIG_SMP.
> 
> This will result in compile errors if code does spinning or yielding for
> non-SMP kernels - which does not make sense to me, so this might actually
> be a nice indicator.
> If you prefer the !CONFIG_SMP implementation let me know and I will respin.

...but I do prefer an implementation for !CONFIG_SMP. I'm tired of fixing
silly compile errors that only happen on s390.